Preheat oven to 375 degrees F. Grease an 8 inch square pan.
Whisk together baking soda, cornmeal, flour and salt. Melt butter in large skillet or in the microwave. Remove from heat and stir in sugar. Quickly add eggs and beat until well blended. Whisk in yogurt. Stir in dry mixture, corn kernels, and onion until well blended and few lumps remain. Pour batter into the prepared pan.
Bake in the preheated oven for 30 to 40 minutes, or until a toothpick inserted in the center comes out clean.